The present invention relates to a shade or color determination apparatus for teeth and dental restorations, and also relates to a method for specifying and determining shades for teeth and dental restorations.
Such a shade determination apparatus and such a method are known from U.S. Pat. No. 5,766,006 (xe2x80x9cthe ""006 patentxe2x80x9d). This solution represents an advance relative to the use of a conventional shade guide. A commercial shade guide has a plurality of color groups, whereby in each group are located teeth with different color saturation and brightness and each group is assigned to a certain shade. The tooth in a shade guide can have a structure of one to five layers.
Such a shade guide has limited selection options. This limitation is not due to a lack of options for producing different color mixtures, but rather to the fact that even experienced dentists are limited in their ability to determine a shade correctly. One reason for this is that the eye becomes fatigued after long periods of comparison. But it is also due to the fact that the eye must observe the natural tooth and the prosthetic tooth held next to it in the shade guide in an xe2x80x9cintegratedxe2x80x9d manner in order to obtain the results of the comparison. As a rule, the tooth in the shade guide has a two-layer structure and an overall thickness of 5 mm, whereby in the incisal region enamel material is applied thicker and in the cervical region dentine material is applied thicker.
An additional problem in the assessability of the reference teeth in the shade guide is that the teeth in the shade guide regularly comprise ceramics fired at high temperatures. Although such ceramics are more cost effective in terms of manufacture, manufacturing costs are substantial since they have to be distributed to all of the dentists. Today, however, it is not unusual for other ceramics to be used that are fired at temperatures lower than, e.g., 1300xc2x0 C. The newest materials for dental restorations always have optical properties that are similar to teeth, e.g., opal effects or brightness values determined by precisely-defined crystal sizes, whereby the optical refraction index is adjusted. Shade guides used in the past are generally not well suited for comparing shades with these new materials. The materials d.SIGN(copyright) and Empress 2(trademark) are also among the new materials that have enhanced brightness even with better translucence. The shade guides that were used in the past are generally not well suited for comparing shades with these new materials.
In this regard, systems like that of the ""006 patent are not helpful because they use the known shade guides as the reference. Since these are not accurate despite the tooth-like structure of their coloration, especially for particularly translucent teeth, however, such computer-supported systems only result in minor improvements despite the expense they involve.
Another problem that in the past could only be addressed unsatisfactorily, if at all, is the progression of both the color and the translucence from the cervical to the incisal region. The cervical region generally has a coloration that tends toward reddish and is a bit transparent. The prior art provides no or only minimal accommodations for this graduation.
The invention relates to a shade determination apparatus and a corresponding method that are able to provide a tooth or a dental restoration in an aesthetically pleasing manner, whereby the shade comparison is made substantially easier for the dentist and laboratory, in particular by easily matching and reproducibly matching the coloration and translucence with adjacent teeth.
The present method is used for determining a patient""s tooth shade for replacement or restoration thereof. This method includes the steps of: generating at least a partial electronic image of a patient""s tooth wherein the image includes color information representative of the patient""s tooth shade; electronically storing color information representative of a plurality of tooth shades in the form of a set of reference templates produced in a layer arrangement and including at least one of layer thickness or material selection; and comparing the color information of the image with the stored tooth shade color information to identify reference templates that may be used to prepare a tooth replacement or restoration having a color that corresponds to the patient""s tooth shade.
The image of the patient""s tooth can be visually or electronically compared to the stored color information. Advantageously, each reference template includes one or more layers of dentine material, incisal material, or opaque material. For optimum results, the comparing of color information and the identification of the reference template(s) is performed by a computer. If desired, the computer can control a CIM apparatus by which the layering of the replacement tooth or restoration to be manufactured can be determined in terms of material selection and layer thickness so that the replacement tooth or restoration can at least be pre-fabricated. The reference templates are preferably made of materials that are fired at the same temperature and same firing curve as the materials that are to be used for the replacement tooth or restoration to provide the closest color match.
A full image of the patient""s tooth may be mapped with color pixels to assist in determining the color of the patient""s tooth shade. Thus, a matching reference template is determined by selecting one or more pixels of the image, which pixels correspond to differential spatial locations of the patient""s tooth, that provide similar color information and electronically comparing that color information with the stored reference template color information to determine the color of that portion of the patient""s tooth. The patient""s tooth pixel colors can be projected onto a display with the reference templates viewable on the display adjacent the patient""s tooth so that optimum visual color matches can be made. Alternatively, the patient""s tooth color can be determined by averaging the color information at selected pixel locations of the image before electronically comparing the averaged color information with the stored reference template color information.
The selection of the pixel(s) and determination of reference template(s) are generally repeated until a tooth shade color is determined for vertical or horizontal partitions, or both, of the tooth and until all the tooth shade color is determined for all spatial locations of the image of the patient""s tooth. Prior to producing the replacement tooth or tooth restoration, the selected reference template(s) can be overlaid on the tooth shape on a display or monitor so that a virtual tooth replacement or restoration can be viewed along with an adjacent tooth or teeth. A digital camera can be utilized to obtain the image of the patient""s tooth and the same camera or similar metamerical conditions can be used to obtain the color information of the reference templates before electronically storing the color information of the reference templates.
The patient""s tooth shade color(s) and selected reference template(s) can be electronically stored on an electronic storage medium which is subsequently forwarded to a dental laboratory for use in construction of a replacement tooth or reconstruction of the patient""s tooth. The electronic storage medium may be transmitted to the dental laboratory over a communications network. The electronic medium includes computer memory, a diskette, or a compact disk and the communications network comprises a computer, e-mail or the internet. If desired, preferred tooth shapes, incisal edges or tooth preparations can be electronically stored to assist the dentist in enhancing the preparation of the patient""s tooth or the shape or incisal edge of the restoration or replacement tooth to provide improved smile appearance or improved biting or chewing performance.
In preparing the dental restoration or replacement tooth, one or a plurality of layers of dentine material, enamel material or opaque material can be applied on a dental alloy to a desired thickness to produce a tooth or restoration having the desired color. Preferably, each layer has a thickness of between about 0.3 and 3 mm and the materials are made of glass-ceramics or fiber-reinforced plastic.